The present invention relates to a copolymer suitable for a molded article, particularly a sheet and a film, a process for producing the same, and a molded article comprising the same.
There have been recently realized progresses such that a polymer having a characteristic different from conventional polymers can be produced according to the appearance of a catalyst using a transition metal compound such as a so-called metallocene or non-metallocene, or the like, and a large quantity of polymer can be produced with an extremely small amount of catalyst.
The application of such catalyst is proposed in the copolymerization of ethylene with an alkenyl aromatic hydrocarbon represented by styrene. For example, a process for producing a quasi-random copolymer of ethylene with styrene (a random copolymer characterized in that methine carbon atoms bonded with a phenyl group are mutually separated by two methylene groups or more) with a so-called homogeneous Ziegler-Natta catalyst using a specified transition metal compound and an organoaluminum compound, is described in Japanese Patent Publication (Kokai) Hei No.3-163088. However, according to these processes, the activity is substantially low in the production of a copolymer having a high styrene content, and a syndiotactic polystyrene is occasionally produced as a by-product, therefore the process cannot be said as an efficient production process.
A process of producing a copolymer using a specified transition metal compound and an organoaluminum compound as a catalyst is reported in Japanese Patent Publication (Kokai) Hei No.9-309925. Said copolymer is a crystalline polymer having a high isotacticity of styrene configuration and occasionally inferior in transparency.
In general, elastic recoverability, delay recoverability, transparency and mechanical strength found in a polyvinyl chloride are required for a copolymer used as a wrap film. However, the polyvinyl chloride comes in question concerning environmental pollution in which the generation of harmful substances during combustion is possible, or the like. Various kind of polymers are presently considered as a replace of the polyvinyl chloride, but it is a status quo that none of them to be satisfied is obtained.
The present invention was achieved in view of the above-mentioned situations. Namely, the objects of the present invention is to provide a copolymer of ethylene with an alkenyl aromatic hydrocarbon, being capable of taking a constitution in which halogen pointed out as a cause for environmental pollution is not contained, and being excellent in elastic recoverability, delay recoverability and vibration suppression performance; a process for producing said copolymer at an extremely high polymerization activity; and a molded article which comprises said copolymer.
In order to attain the above-mentioned objects, the present inventors have intensively studied a copolymer of ethylene with an alkenyl aromatic hydrocarbon which is based on a production process using a transition metal compound represented by a metallocene as a catalyst component, and completed the present invention.
Namely, the present invention relates to a copolymer of ethylene with an alkenyl aromatic hydrocarbon wherein the content of the alkenyl aromatic hydrocarbon in the copolymer is 0.2 to 60 mol % and the ratio ({circle around (2)}/{circle around (3)}) of the area of a peak {circle around (2)} appearing at 34.0 to 36.0 ppm in a 13C-NMR spectrum of the copolymer to the area of a peak {circle around (3)} appearing at 36.0 to 38.0 ppm is 0.01 to 0.35 and a molded article comprising said copolymer.
And, it relates to a copolymer has a structure in which carbon atoms substituted with an aromatic hydrocarbon group are mutually separated with one methylene group, a structure in which they are separated with two methylene groups, and a structure in which they are separated with at least three methylene groups, in the backbone (main chain) of the copolymer in the copolymer described above and a molded article comprising said copolymer.
Further, the present invention relates to a process for producing the copolymer described above, and a process for producing the copolymer which comprises copolymerizing ethylene with an alkenyl aromatic hydrocarbon in the presence of a catalyst prepared by using (A), and [(B) and/or (C)] described below:
(A) a transition metal complex represented by the following general formula [I]: 
xe2x80x83(wherein M1 indicates a transition metal atom of the Group IV of the Periodic Table of the Elements; A indicates an atom of the Group XVI of the Periodic Table of the Elements; J indicates an atom of the Group XIV of the Periodic Table of the Elements; Cp1 indicates a group having a cyclopentadiene type anion skeleton; each of X1, X2, R1, R2, R3, R4, R5 and R6 independently indicates a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an aryl group, a substituted silyl group, an alkoxy group, an aralkyloxy group, an aryloxy group or a di-substituted amino group; and R1, R2, R3, R4, R5 and R6may be optionally combined with each other to form a ring);
(B) one or more aluminum compounds selected from the following (B1) to (B3);
(B1) an organoaluminum compound represented by the general formula E1aAlZ3xe2x88x92a,
(B2) a cyclic aluminoxane having a structure represented by the general formula {xe2x80x94Al(E2)xe2x80x94Oxe2x80x94}b, and
(B3) a linear aluminoxane having a structure represented by the general formula E3{xe2x80x94Al(E3)xe2x80x94Oxe2x80x94}cAlE32 
(wherein E1, E2 and E3 respectively represent a hydrocarbon group, all of E1, all of E2 and all of E3 may be the same or different; Z represents a hydrogen atom or a halogen atom, and all of Z may be the same or different; xe2x80x9caxe2x80x9d represents a number satisfying the expression 0 less than axe2x89xa63; xe2x80x9cbxe2x80x9d represents an integer of 2 or more and xe2x80x9ccxe2x80x9d represents an integer of 1 or more); and
(C): a boron compound of any one of the following (C1) to (C3);
(C1) a boron compound represented by the general formula BQ1Q2Q3,
(C2) a boron compound represented by the general formula G+(BQ1Q2Q3Q4)xe2x88x92, and
(C3) a boron compound represented by the general formula (L-H)+(BQ1Q2Q3Q4)xe2x88x92
(wherein B represents a boron atom in the trivalent valence state; Q1 to Q4 may be the same or different and respectively represent a halogen atom, a hydrocarbon group, a halogenated hydrocarbon group, a substituted silyl group, an alkoxy group or a di-substituted amino group; G+ represents an inorganic or organic cation; L represents a neutral Lewis base; and (L-H)+ represents a Brxcfx86nsted acid).